The present invention concerns tires with radial carcass reinforcement and, in particular, the protection of their crown reinforcement.
Tires intended to roll under difficult conditions, for example, on road surfaces containing stones or sharp objects, usually present a crown reinforcement comprising a working block and, radially outward, a protective block. The working block is intended to absorb the stresses due to inflation and rolling of the tire and comprises at least two superposed plies of cords parallel in each ply and crossed from one ply to the next by forming angles (xcex1, xcex2) with the circumferential direction ranging between 10xc2x0 and 45xc2x0.
The protective block is intended to protect the plies of the working block from damages due to shocks and perforations sustained in use and comprises at least one ply of parallel wires. Said cords often have an elongation at rupture exceeding that of the working plies they protect.
In order to improve the endurance of the crown reinforcement of such a tire, application WO 96/20095 discloses a tire comprising a crown, two sidewalls and two beads, a carcass reinforcement anchored in the two beads and a crown reinforcement, said crown reinforcement including radially, from inside outward, a working block with at least one ply of parallel cords of circumferential orientation and one protective block with at least one ply of parallel cords of elongation at rupture greater than that of the cords of the ply of circumferential orientation of the working block, in which said working block comprises radially, from inside outward, a triangulation ply of wires oriented at least 60xc2x0, two working plies formed by inextensible wires oriented at angles ranging between 10 and 45xc2x0 and said ply of parallel cords of circumferential orientation of the working block placed between the two working plies, and in which the cords of the ply of the protective block have an orientation similar to that of the cords of the adjacent working ply of the working block.
The object of the invention is another tire architecture also making it possible to improve substantially the endurance of the crown reinforcement and, notably, its resistance to shocks, perforations and oxidation due to rolling over road surfaces containing sharp stones.
The following meanings apply:
xe2x80x9ccordxe2x80x9dxe2x80x94monofilaments as well as multifilaments, or assemblages like cables, yarns or even any type of equivalent assemblage, whatever the material and treatment of said cords, like surface treatment or coating or precoating, for example, in order to promote adhesion on the rubber;
xe2x80x9cinextensible wirexe2x80x9dxe2x80x94a cord having a relative elongation less than 0.2% measured under 10% of its breaking load;
xe2x80x9celastic wirexe2x80x9dxe2x80x94a cord having a relative elongation greater than 0.5% measured at 10% of its breaking load;
xe2x80x9ca circumferentially oriented cordxe2x80x9dxe2x80x94a cord oriented roughly parallel to the circumferential direction of the tire, that is, forming an angle with that direction in the +2.5 to xe2x88x922.5xc2x0 range and around 0xc2x0;
xe2x80x9ca radially oriented cordxe2x80x9dxe2x80x94a cord contained roughly in the same axial plane or in a plane forming with an axial plane an angle less than or equal to 10xc2x0.
The tire, according to the invention, comprises a crown, two sidewalls and two beads, a carcass reinforcement anchored in the two beads and a crown reinforcement. The crown reinforcement comprises radially, from inside outward, a working block and a protective block. The working block has at least two superposed working plies formed by cords parallel in each ply and crossed from one ply to the next by forming angles (xcex1, xcex2) with the circumferential direction ranging between 10xc2x0 and 45xc2x0 and one ply of parallel cords of circumferential orientation. The protective block has at least one ply of parallel cords of elongation at rupture greater than that of the cords of the ply of circumferential orientation of the working block. Said tire is characterized in that the ply of parallel cords of circumferential orientation is the radially outermost ply of the working block, in that the parallel cords of the ply of the protective block have a circumferential orientation and in that the ply of parallel cords of circumferential orientation of the working block has an axial width less than the axial width of the narrowest of the working plies, as well as than the axial width of the ply of cords of circumferential orientation of the protective block.
The circumferential orientation of the protective ply and of the adjacent ply of the working block, as well as the fact that the ply of the crown reinforcement whose axial width is narrowest is the ply of cords of circumferential orientation of the working block, make it possible to improve remarkably the resistance to shocks, perforations and oxidation resulting therefrom of the crown reinforcement of the tire according to the invention.
Preferably, the ratio of elongation at rupture between the cords of the ply of parallel cords of circumferential orientation of the protective block and the cords of the ply of parallel cords of circumferential orientation of the working block is greater than 1.5. This makes it possible for the cords of the protective ply not to be under stress on normal rolling and thus to be fully effective in resisting any penetration.
The axial width of the ply of cords of circumferential orientation of the protective block ranges advantageously between the axial width of the narrowest working ply and the axial width of the widest working ply.
The circumferentially oriented ply of the working block can be formed by elastic cords, presenting a curve of tensile stress as a function of relative elongation having low gradients for slight elongations and a roughly constant and steep gradient for greater elongations. Said ply can also be formed by cords circumferentially oriented and cut so as to form sections of length much less than the circumference of the ply. But, in order to obtain an excellent absorption of circumferential stresses, that ply can consist of inextensible wires.
The ply of the protective block can be formed by elastic wires or textile yarns such as aramids.
The two plies of parallel cords of circumferential orientation can also be formed in textile yarns, notably, aramids.
The characteristics and advantages of the invention will be best understood by means of the description which follows and refers to the drawing, nonlimitatively illustrating working examples.